Fiber to the premises/business/home (i.e., FTTx) provides broadband data transfer technology to the individual end-user. FTTx installations, which are being increasingly deployed throughout the world, are making use of innovative, reduced-cost system designs to promote the spread of the technology. For example, fiber may be delivered in the last link by way of a microcable. Air-blown fibers provide another efficient model for delivering the link to the end-use terminus. There continues to be industry-wide focus on modes of deployment that overcome economic obstacles that impede fiber-based broadband solutions for data transmission to businesses and residences.
Cost-effectiveness is important, of course, for achieving successful FTTx systems. Reduced size for cables, drops, and structures for blowing are often critical, too. Installation of conduits suitable for traditional cable designs is often prohibitive in existing infrastructure. Thus, existing small ducts or tight pathways have to be used for new fiber installations. Low-cost and reduced-size requirements are driving in a direction that reduces protection for the optical fibers (i.e., away from conventionally robust, more bulky cable designs).
Glass designs are now available that offer reduced sensitivity to small bending radius (i.e., decreased added attenuation due to the phenomenon known as macrobending). These include trench-assisted core design or void-assisted fibers. Glass designs with lower mode field diameter are less sensitive to macrobending effects, but are not compatible with the G.652 SMF standard. Single-mode optical fibers that are compliant with the ITU-T G.652.D requirements are commercially available, for instance, from Draka Comteq (Claremont, N.C.).
Microbending is another phenomenon that induces added loss in fiber signal strength. Microbending is induced when small stresses are applied along the length of an optical fiber, perturbing the optical path through microscopically small deflections in the core.
In this regard, U.S. Pat. No. 7,272,289 (Bickham et al.), which is hereby incorporated by reference in its entirety, proposes an optical fiber having low macrobend and microbend losses. U.S. Pat. No. 7,272,289 broadly discloses an optical fiber possessing (i) a primary coating having a Young's modulus of less than 1.0 MPa and a glass transition temperature of less than −25° C. and (ii) a secondary coating having a Young's modulus of greater than 1,200 MPa.
Nonetheless, better protection against microbending is still needed to help ensure successful deployment in more FTTx applications. To this end, it is necessary to discover and implement new coating systems that better address the demands FTTx installations place on fiber and cable structures in a way that is commercially practical (i.e., cost-effective).
As compared with traditional wire-based networks, optical-fiber communication networks are capable of transmitting significantly more information at significantly higher speeds. Optical fibers, therefore, are being increasingly employed in communication networks.
To expand total transmission throughput, optical-fiber network providers are attempting to place ever more optical fibers in ever-smaller spaces. Packing fibers into tight spaces, however, can cause undesirable attenuation. Indeed, there is an inherent trade-off between increased fiber density and signal attenuation.
Fiber optic cables are commonly deployed in ducts (e.g., ducts having an outer diameter of about 42 millimeters). Traditional duct installation, however, uses space inefficiently. The typical capacity of such ducts has been one cable per duct, although in some cases two cables have been installed.
In this regard, it is desirable to achieve optical-fiber cables having a reduced diameter such that multiple (e.g., three) optical-fiber cables can be installed in a duct. It is also desirable to achieve optical-fiber cables having a high fiber density. Moreover, it is desirable to achieve high-fiber-density optical-fiber cables having satisfactory attenuation performance.
Additionally, it is desirable for optical-fiber cables deployed in ducts to be robust enough to withstand mechanical stresses that may occur during installation. Such optical-fiber cables should also be able to withstand conditions of use over a wide temperature range, such as between about −20° C. and 50° C. Indeed, it is desirable for optical-fiber cables to be able to withstand an even wider temperature range, such as between about −40° C. and 70° C.